Curing butyl rubber latex films



United States tea 3,005,804 CURING BUTYL RUBBER LATEX FILMS Alfred L.Miller, Cranial-d, Anthony J. Petro, Elizabeth,

and Kenneth W. Powers, Nixon, Ni, assignors to Esso Research andEngineering Company, a corporation of Delaware No Drawing. Filed Dec.17, 1958, Ser. No. 780,942

Claims. (Cl. 260-795) This invention relates to the preparation of avulcanizable gum butyl rubber. It relates more particularly to thepreparation of a vulcanizable butyl rubber latex designed for use asfilms and in the impregnation of articles which are dried out and thenheated to a sufficiently elevated temperature to lead to a productassociated with butyl rubber in a high state of cure.

It is known to vulcanize natural rubber latices with sulfur in thepresence of various accelerators. The same accelerators which are usedto vulcanize pigment-loaded stocks are generally suitable 'for thispurpose.

However, when pigment-loaded butyl rubber stocks are vulcanized it hasbeen recognized that the accelerators generally used for natural rubberand synthetic rubbers such as SBR (formerly GRS) are unsuitable. Whenlattices or other gum stocks of butyl rubber are cured, even moredifiiculty is found and accelerators useful for curing loaded butylstocks fail to produce a cure in either latex or gum stocks.

In accordance with one embodiment of the present invention, it has nowbeen discovered that latices of butyl rubber can be vulcanized to a highstate of cure by the use of zinc diethyldthiocarbamate. Otheraccelerators give either no cure at all or give vulcanized productswhich have such poor physical properties as to be unsuited tor practicaluse.

In accordance with another embodiment of the invention, the tensileproperties of the vulcanizates obtained by the use of zincdiethyldithiocarbamate are improved by the addition of 2 to 4 parts,perhundred parts of rubber, of an ammonium halide, a polysubstitutedamine halide, a polysubstituted ammonium halide, or the zinc salt ofmercaptobenzothiazole. Still further improvements in the tensiles can beachieved by allowing the compounded latex to stand for about 24 hoursprior to vulcanizing.

The butyl rubber latices used in the practice of this inventionaredispersions of vulcanizable elastic copelyiners of isobutylene andsmall amounts of diolefins. Butyl rubber is thus defined in HaakhsChemical Dictionary, 3rd edition, page 151. Its properties and method ofpreparation are amply described in Synthetic Rubber by Whitby (JohnWiley and Sons, 1954), pages 838-391, where it is pointed out thatdiolefins containing 4 to 6 carbon atoms such as butadiene(methylbutadiene) piperylene and isoprene are suitable for reacting withthe isobutylene.

The rubber is prepared as a solid crumb and is converted into a latex bydissolving in a hydrocarbon solvent such as hexane. Latices are suitablyprepared from this solution by emulsifying with water inthe presence ofan alkali metal, alkaline earth metal, amine or ammonium salt of a C -Corganic sulfate and a monovalent salt of dihydrogen orthophosphate. Forexample, a typical recipe for the preparation of these latices is asfollows:

Parts Solution ot-butyl rubber in hexane (23 wt.

N.V.M.) 50-70 prepared by dipping 3,005,804 Patented Oct. 24., 1961 "iceif desired the above typically compounded latex may be aged overnightprior to curing. In any case films are a form of the latex and dryingthe dipped films at 160 F. for about one hour. The dried film is thencured at 250-260 F. for one hour.

The following examples are given to aid in understanding the invention,but it is to be understood that p the invention is not limited to theingredients or proportions set forth in the examples.

Example 1 A butyl latex was prepared by emulsifying a. 23% N.V.M.solution of butyl rubber in hexane with water in the presence of 5 parts(per hundred parts of rubber) of the sodium salt of sulfatednonylphenoxye'thoxyethanol and 1 part (per parts of rubber) of sodiumdihydrogen phosphate. The pH of this latex was adjusted to 9 by additionof NH OI-l and the resulting mix was compounded with various amounts ofzinc diethyldithiocarbamate and zinc dimethyldithiocarbamate. Films werethen prepared by dipping forms at a rate of 5 inches per minute in threesuccessive dips, each dip being dried for 1 hour at 160 F. After thefinal dip the films were cured at 2502260 F. for one hour. The followingdata were obtained.

Compound 1 2 3 4 Latex solids pts. by wt" 100 100 100 100 Z110 (10.-.. 55 5 5 S (10..-- 2 2 2 2 Ethyl Zimate (10...- 2 3 4 Methyl Zimate do 3Av. Ifilrn Thickness mils 15 16 15 18 Tensile p.s.i 1, 825 2,020 2, 660Elongation percent 1, 035 1, 040 1, 010 1, 300

Example 2 The latex of Example 1 was compounded with variousconventional accelerators used for commercial high unsaturated rubbersknown as SBR (formerly GRS), natural rubber, etc. and films formed asbefore. The fol- These data show that the presence of 1-2 Wt. percentlowing data were obtained: of an amine hydrochloride or ammoniumchloride in a Compound 1 2 3 4 5 6 3 Rotax L d ftncceleratolr 522 fl d 2240 3.555.

timate ens e p.s. Elongation percen 1,085 1,300+ cure cute 1 Zimate iszinc dialkyldithioearbamate. 4 Mercaptobenzothiazole.

2 Zine salt of mercaptobenzothiazole.

* Benzothiazyl disulfide.

the tensiles were very poor.

Of this group only zinc diethyldithiocarbamate was found to cure butylrubber latex satisfactorily.

Example 3 p The experiment of Example 1 was repeated except that variousamounts of amine hydrochlorides and ammonium 5 Plpertdiniumpentamethylene dithiocarbamate.

butyl latex film cured with zinc diethyldithiocarbamate greatlyincreases the tensile strength of the cured film.

Example 4 The experiment of Example 3 was repeated except that zetax wasadded in conjunction with ethyl zimate.

The following results were obtained:

Compound 1 2 3 4 5 Latex solids pts. by wt 100 100 100 100 100 100 100100 100 Zn 5 5 5 6 5 5 5 5 6 S 2 2 2 2 2 2 2 2 2 Ethyl zimate 3 3 3 3 33 0 Zetax 9 d0 0 1 2 3 3 Cure Temp F 260 250 260 240 260 240 260 240 260Tensile, p.s. 2, 235 1, 260 3, 040 2, 270 2, 905 2, 395 2, 770 2, 185}N0 Elongation "percent- 1, 010 1, 110 835 1, 050 810 1, 020 805 1, 020cure.

1 Zinc dlethyldithiocarbamate.

chloride were added to the recipe in conjunction with ethyl zimate. Thefollowing data were obtained on the Zinc salt of mercaptobenzothiazole.

The above results show that the zinc salt of mercaptobenzothiazolepromotes the cure of butyl latex with zinc cured fildiethyldithiocanbamate, giving stronger films at lower elongation at 260F. At 240 F. it gives films having Compound 1 2 3 4 strengths equivalentto those at 260 F. without it. At 250 F. without zetax the fihns arevery poor. Run No. Lag}; solids by Wt 2 10g g 10g 5 shows that no cureis obtained with zetax in the absence Z o S? 2 2 2 2 of ethyl Example 5Ethyl zirnate 1 1 2 3 3 Nmoi "do -n 3 The experiment of Examle 3 wasrepeated except that iiifiltaaaijiti 135221123: 1:195 1:045 1:065 1:015Vamps amounts of sodium and potassium chlonde were added to the recipeinstead of the NH CI 1 Zinc diethyldltmocarbamate; and amine salts. Thefollowing data were obtained:

Compound 1 2 3 4 5 6 7 8 100 100 100 100 100 100 5 5 5 5 5 5 2 2 2 2 2 23 3 s 3 a a 2 a Zine diethyldithiocarbamate.

These data show that no desirable effect on tensile Compwld 1 2 3 4strength is obtained by the addition of either potassium or sodiumchloride. Latex solids .pts. by wt, Z110 0 Example 6 E'tifil'iffiizit grc l flfl Dry gum butyl rubber was press cured in the presence DCAHCITensile, ..p.s.t 2, 79 Elongation "percent" 1, 010 925 1 Zincdiethyldithiocarbamate. Diethylamine hydrochloride.

I Dicyclohexylamine hydrochloride.

of sulfur and zinc diethyldithiocarbamate with the addition of ammoniumchloride and diethylamine hydrochloride in comparative runs. Thefollowing data were obtained:

Compound 1 2 3 4 5 6 Butyl rubber -pts. by wt.- 100 100 100 100 100 100ZnO (10---- 5 5 5 5 5 5 (10.--. 2 2 2 2 2 2 Ethyl zlmat (10.--. 3 3 3 33 3 DEAECI do 1 2 6 Modulus 300%. -.p.s.i.-- 115 105 110 130 125 75Modulus 500% p.s.l 195 175 190 245 240 155 Tensile p.s.l 2, 410 2, 6852, 405 3, 450 3, 195 1, 115 Elongation percent. 87 87 830 865 895 835 1Zinc diethyldithiocarbamate.

9 Dlethylamine hydrochloride.

The above data show that while 1% of ammonium chloride results in aslight improvement in the tensile Control Zparts strength, 1 part of thediethylamine hydrochloride is out- NHCD NHO1 standing, the tensilestrength increasing from 2410 to 4h N 24 h 3450. Even two parts givesexcellent results. No age age Gage a e Example 7 gltimage tensile on aion 1,

When the experiment of Example 4 is repeated for g loaded stocks, theoutstanding improvement of diethylamine hydrochloride is no longerobtained as illustrated 25 by the following data:

The above data show that improved results are obtained by aging thecompounded latex for 24 hours prior to curing, even in the absence of NHCI.

o p 1 i 2 l 3 4 5 The nature of the present invention having been thus 1be fully set forth and specific examples of the same given, Buty rub rpts. by wt 100 100 100 100 100 Phflmck A 25 25 25 25 25 what 1s claimedas new and useful and desired to be geelertixau 2% 2? 2i 2? secured byLetters Patent 1s:

1 Zinc 0Xide 1o., 5 5 5 5 1. Sulfur vulcanized gum butyl rubbercopolymer of fi ggf- 3 isobutylene and a small amount of a diolefin,containing g i r c go... 1.2 1. 4 to 6 carbon atoms containingas avulcanization acd g 6Z 1' jj 290 210 ""gg' 270 celerator l to 6 parts bywt. of zinc diethyldithiocar- 1 8% $33 1 8 328 bamate per 100 parts bywt. of rubber and 2 to 4 parts 0- 1 y en 2, 225 2,120 2,300 2,110 by wt.of ammonium chloride per 100 parts by wt. of Elongatlom. 585 625 585 5954,0 rubber 1 Zinc diethyldithiocarbamate. 2 Tellurium diethyldithiocarbamate. B Diethylamine hydrochloride.

Example 8 The butyl rubber latex of Example 1 was compounded accordingto the following recipe:

Parts Latex solids 100 Zinz ox 5 Sulfur 2 Zinc diethyldithiocarbamate 3NH Cl 2 the compounded latex was allowed to stand overnight beforepreparing a film as described in Example 1 and curing at 250-260 F. forone hour in a hot air circulating oven. Films were prepared from theother portion immediately and cured. The following results were obtainedand compared with the cured films obtained in which no NH Cl had beenincluded in the recipe:

One portion of 2. In the process of vulcanizing with sulfur gum butylrubber copolymer of isobutylene and a small amount of a diolefin,containing 4 to 6 carbon atoms, the step which comprises heating a gumbutyl stock in the presence of 1 to 6 parts by wt. of zincdiethyldithiocarbamate per 100 parts by wt. of rubber and 2 to 4 partsby wt. of diethylamine hydrochloride.

3. The process of vulcanizing butyl rubber latex copolymer ofisobutylene and a small amount of a diolefin, containing 4 to 6 carbonatoms which consist in mixing the latex with 1 to 11 parts by wt. ofzinc oxide, 2 parts by wt. of sulfur and 1 to 6 parts by wt. of zincdiethyldithiocarbamate per 100 parts by wt. of rubber and 2 to 4 partsby wt. per 100 parts by wt. of rubber of a compound chosen from thegroup consisting of ammonium chloride, diethylamine hydrochloride, anddicyelohexylamine hydrochloride, forming a film from said latex andheating said film at 250260 F. for about one hour.

4. Process according to claim 3 in which the compound is ammoniumchloride.

5. Process according to claim 3 in which the compound isdicyclohexylamine hydrochloride.

6. Process according to claim 3 in which the compound is diethylaminehydrochloride.

7. The process of vulcanizing butyl rubber copolymer latex ofisobutylene and a small amount of a diolefin, containing 4 to 6 carbonatoms which consist in mixing the latex with 1 to 11 parts by weight ofzinc oxide, 2 parts by weight of sulfur and 1 to 6 parts by wt. of zincdiethyldithiocarbamate per 100 parts by wt. 75 of rubber and 2 to 4parts by wt. per 100 parts by wt.

of rubber of a compound chosen from the group conride, anddicyclohexylamine hydrochloride, maintaining said mixture at roomtemperature for at least 24 hours, forming a film from said mixture andheating said film at 250260 F. for about one hour.

8. Process according to claim 7 in which the compound is ammoniumchloride.

9. Process according to claim 7 in which the compound isdicyclohexylamine hydrochloride.

10. Process according to claim 7 in which the compound in diethylarninehydrochloride.

sisting of ammonium chloride, diethylamine hydrochlo-.

References Cited in the file of this patent UNITED STATES PATENTS2,356,128 Thomas et al Aug. 22, 1944 2,391,742 Roberts -Dec. 25, 1945FOREIGN PATENTS 743,731 Great Britain Jan. 25, 1956 734,390 GreatBritain July 27, 1955 OTHER REFERENCES Wilson: British CompoundingIngredients for Rubber, Heifer & Sons Ltd.,

Cambridge (1958), pp. 10, 11, 45-47 and 361-362.

1. SULFUR VULCANIZED GUM BUTYL RUBBER COPOLYMER OF ISOBUTYLENE AND ASMALL AMOUNT OF A DIOLEFIN, CONTAINING 4 TO 6 CARBON ATOMS CONTAINING ASA VULCANIZATION ACCELERATOR 1 TO 6 PARTS BY WT. OF RUBBER AND 2 TO 4PARTS BAMATE PER 100 PARTS BY WT. OF RUBBER AND 2 TO 4 PARTS BY WT. OFAMMONIUM CHLORIDE PER 100 PARTS BY WT. OF RUBBER.